The long term objective of this work is to define the role of the cerebellar cortex in motor behavior. The first goal is to describe the kinematic parameters represented in both the simple and complex spike discharge of Purkinje cells during multi-joint, two dimensional, visually guided arm movements in the primate. In different areas of the cerebellum, the "movement fields" of Purkinje cells will be determined for movements of different distances and directions throughout the horizontal plane. Whether the responses are defined in a head/body or hand centered reference frame will be evaluated. The correlation of the simple and complex spike response with the movement kinematics and electromyographic activity will be determined. The second series of studies will evaluate the role of cerebellar Purkinje cells in the feedforward and feedback control of visually guided limb movement. Introduction of visual feedback errors during the arm movement in primates will permit introduction of quantitative errors into the movement. In these experiments the discharge of Purkinje cells and its correlation with either the movement parameters or the errors introduced into the visual feedback loop will be determined. The cerebellum has been hypothesized to play a significant role in motor learning. Experiments are proposed to evaluate this hypothesis in voluntary, motor learning. In this last set of studies the discharge of Purkinje cells will be evaluated during the motor learning required to compensate for visual feedback disparity during visually guided arm movements. Analysis of the simple and complex spike discharge prior to, during and after learning and the relationship of the discharge to the kinematic changes associated with learning will be determined.